Thermally actuated double throw switch mechanism



June 30, 1964 D FALLON ETAL 3,139,500

THERMALLY ACTUATED DOUBLE THROW SWITCH MECHANISM Filed March 2, 1960 JOHN /7 C14/V72 l/V.

United States Patent (,O,

The present inventionprelates to an improved electric switch mechanism particularly suitable for operation by a thermally responsive element.; n 'Y One Yobject of the present invention iis the provision of an electricv switch which maybe of the double-throw type v operatedV bya snap acting ythermally responsive element which suddenly reverses its form in response to temperature,r changes and which provides movement in excess of that required for Vactuating lthe vmovable vswitch contact,

the connection between the thermally responsive element and movable switch contact being yieldable to permit a relativelyl free normal amplitude of movement of the element so that its responsiveness to temperature changes is unaffected by confining stresses..

Another object of the invention is the provision of an improved switch comprising a flexible contact arm which is flexed to engage and disengage a fixed contact, the contact arm being moved from engagement with the fixed contact by a .relatively rigid actuator member rigidly attached thereto at an area adjacent to the point at which the arm vengages the contact so that when the actuatoriis moved in a direction in which the contact arm flexes and the contacts tend to stick due to welding, for example, the: actuator ,pivots about the contact and rocks or twists the arm at the point of its engagement with the fixed contact, thereby breaking the weld by use of a relatively low force. The contact arm may move between two fixed contacts to provide a double-throw switch and the twisting action described occurs at each contact position.

,A further object of the invention is to provide a switch structure of the character mentioned having a doublethrow contactarrangement and in which the actuator lies alongside the contact arm and hasa heelrportion which engages a stop so that an operating element acting on the actuator `and exerting a force in excess'of that required Vto viiex the` contact arm frornone xedfcontact to the other can overtravel relative to the arm byl moving the actuator to separate the heelportion from the arm. The actuator then maintains the arm closed on the last mentioned Vfixed contact although the operating element may initially gradually shift toward the other switch position, .and then'upon snap movement of the operatingelenient toward the other position, the heel portion of the actuator strikes the arm thereby imparting a hammer-like action to the arm toV cause it to positively and quickly shift from the last engaged contact to the other.

The improved switch structure assures positive switch operation` by a minimum of force on the actuator, and provides for yielding'overtravel'of the actuator so that the actuator may be operated by a condition responsive device havingA a response travel appreciably in excess of the travel required to actuate the switch and which may be of the type which has an initial relatively slow or creeping movement followed by a snap movement, such as a snap acting bimetal.

These and other aspects ofthe invention will become more readily apparent upon examination of the followingdetailed description together with the accompanying drawings, in which: g r g FIG. 41 is a cross-sectional view of a double-throw switch embodying the invention;

FIG. 2 is a cross-sectional view'similar to FIG. l but showing a partial Welding of the contacts and an initial movement of the contact arm in shifting from the position shown inFIG. 1 to its alternate position;

Y FIG. `3 is a View similar to FIG. 2 showing the contact arm of the switch shifted to itsalternate position;

FIG. 4 is a top, fragmentary View of the switch showing the relationship of the switch terminals and the contact portions thereof; and f FIG. 5 is a plan view of a bimetal element of mechanism.

this switch n Referring to the drawings, reference numeral indi- Y' cates a thermallyresponsive switch constructed according to the present invention and which includes a generally cylindrical housing or frame 12 of suitable molded insulating material and which supports terminals 14, 16 and .18 attached thereto by rivets 20. Terminalv 14 providesl a bridge portion 14a to which one end of a flexible con.

tact arm 22 is attached, the arm having laterally projecting lugs 22a and 22b which rest on and are attached. to the terminal by the rivets 20, as shown in FIG. 4. A downwardly turned flange'ZZc cooperates With the leftA hand edge of terminal 14 to position the arm. The opposite end of arm 22 carries oppositely facing contacts4 23 and 24 whichv alternately engage fixed spaced contacts 25 and 26 attached to terminals 16 and 18, respectively,

as" shown. Contact arm 22 may be formed of any suitable spring material having good electrical properties,

such as beryllium copper or Phosphor bronze, and is normally biased to close contact 23" on fixed contact 25 but maybe iiexedV upwardly 'tov'engage Vcontact 24 with con-l tact 26. y

Contact arm 22 is exed upwardly, as viewed in the drawings, to separate contacts 23 and 25 and to close contacts `24 and 26 by an actuator 28 which is moved by an operating element 30 in they form of a snap acting bi-` Actuator 28 comprises an elongated bar-like;

metal; member which is rigid as compared to the contact arm and which extends generally parallel to the arm and isV firmly attached thereto at the point between contacts 23 and 24. This arrangement is such that actuator 28 ist urged toward contact arm 22 by the resiliency ofV thelatter and the left hand end thereof isnormally spaced lfrom the arm by a heel portion or ridge 29 formed therein whichengages'the end of the Contact arm at tached to terminal 14, as seen in FIG. l. In the form of theinvention shown a thermally responsive element 30 ,operates actuator 28 in response to predetermined changes I in temperature and comprises a snap acting type bimetal member which is dish-shaped and is normally bowed or' dished downwardly when below a given temperature and which reverses its curvature to bow upwardly' withv a` quick, substantial movement upon attaining thel given der gree of temperature. Such snapacting devices and variarAf tions thereofy are wellknown in the'art and any suitable v type may be employed. Element 30`is disposed in the Q lower part of housing 12 so as to freely reverseits form,

and the periphery thereof is loosely disposed between an.. annular shoulder 31 and a circular metal cover plate 32.'A crimped overa shoulder'aformed about the lower end of the'hou'sing 12;

Actuatori28 is connected with element 30 by a plunger i ,Y 33 which is guided vertically by the edges of an opening r 34d in a partition 34fsecured inside housing 12, and the the actuator.

plunger is engaged by a central tongue 30a formed on 'element 30 when the element exes upwardly, as is de-A Lscribed more fully hereinafter. e

' With speciiic reference to FIGS. 1-3, the operation of the switch is shown 'in' sequence as would-'occur should contacts 23 and 25 tend to' stick, as will occur by arc welding. As plunger 33 is `pushed upwardly by tongue 30a upon snap movement of bimetallic element 3G, it acts upon the intermediate portion of the rigid actuator member 28 to cause the free end thereof to swing upwardly in a direction generally parallel to a line between contacts 25 and 26. Thisinitial upward movement of the free end of actuator 28 lcauses the actuator to pivot about contact y25, which pivoting' provides a rocking or twisting action of contact 23 on contact 25,`there by readily breaking the weld. Atthe same time, vupward movement of the freeV end of actuator 28 causes some ilexing of the resilient arm 22 to Itheleft which shortens its eiective length thereby tending todraw contact 23 slightly to the left, as it is twisted from contact 25. Further upward movement of plunger 33 causes actuator 28 Yto fiex contact arm 22 upwardly and engage contact 23 with contact 26. It will be appreciated that as a practical vmatter the movement of contact arm 22 from contact 25 to contact 26 takes place with a snap action due to the l snapmovement of element 30.

It is'lto be noted that after contact arm- 22 engages contact 26, actuator 28 may be further yieldingly pivoted about the engaging portions of contacts 23 and 26 so that but slight resistance is offered to tongue 30a of bimetal Yelement 30 in its upward ilexure, Ywhich permits the bimetal'to assume a more or less `runrestrained reversed curvature. We have found that ifthe bimetal is confined and limited in itsfmov'ement to lessthan its norr`malV amplitude, stresses are imposed thereon which tend anywelded connection which might have been formed. v Simultaneously, resilient contact arm 22 is ilexed somel whatfrom its straight-line position so ,thatra wiping action between the contacts 23 and-26 takesV place. As

disc 30 snaps to its position of curvature shown'in FIG. yl,

the spring force stored in contact arm 22 by its initial yupward deflection, causes the contact arm to follow the snap action of the disc and to. bring about a snap action connection between contacts 23 and 25. v

.It will be noted thatby the construction disclosed, initial slight movement of tongue 30a of element 30 does notappreciably lessen the contact pressure between contacts 24 and 26, and the separation of these contacts occurs only afterV the bimetal `has commenced itsV snap action. This is likewise truewith respect to movement of the bimetal and switch parts in the opposite direction inas- .K much as tongue 30a is below plunger 33 duringthe initial pre-snap movement of the tongue.

One of the features of the invention is that the switch may be actuated by using a relatively low. actuation force. This is due to the twisting or rocking movement imparted to the closed contacts by actuating member 28, thereby obviating the need ,for high forces in breakingpartially scope of the invention as dened in the appended claims.

We claim: Y 1. A switch mechanism comprising: (a) support means, W (b) a fixed contact mounted on said support means, (ci) a flexible spring arm having one end secured to said support means, (d) a movable contact carried on the other end of saidl spring arm and normally urged by said springi arm in arst direction toward said ixed contact,

(e) an elongated actuator member formed of a rela-v tively rigid material with respect to said vspring arm and having one end fixed to the end of said spring arm on which said movable contact is carried, and extending along one side of said spring arm remote from said xed contact and having thevother end' terminating adjacent said one end of said springv arm` .and being movable laterally therefrom,

` (f) said spring arm normally biasing said actuator 'y' member rrtoward said spring arm, kand r (g)` means for applying a moving force to said actuator `member between the ends thereof in a direction opposite to saidrone direction so as to tend to separateV l, said other end of said actuator member fromk said` spring arm and ilex said contact carrying end of saidv spring arm to impart a rolling action of said movable contact ony said Iixed contact before said movable'l contact is moved away from said xed contact. r 2. A switch mechanism comprising:

(a) support means,

said support means,

(d) a movable contact carried on the other endY of said spring armand normallyL urged by said spring arm;

- in a iirstdirection toward'said fixed contact, ,(e) an elongated actuator memberformed Lof a relatively rigid material with respect to said spring army and having one end tixedV to the end of said spring arm on which said movable contact is carried,

' said actuator being disposed along the side of said spring arm remote from said fixed contact and terminating with its other end adjacent said one end of said spring arm,

v(g) said spring arm normally biasing said actuator member toward alignment against said Vspring arm, (h) means for applying a moving force to said actuator member between the ends thereof ina direction opposite to said one direction so as to tend to separate said actuator member from said spring arm and to flex said spring arm before said movable contactis moved away from said xed contact, (i)` said support means comprising stopy means adja- V cent said one end of said spring arm, and Y i (j)" said other end of said actuator member terminat-n ing in a heel portion, v (k) said heel portion being disposed adjacent said stop means for engagement therewith during movementA of said movable contact toward said xed contact upon withdrawall of said force whereby said actuator arm is caused to pivot about said vheel portion and accelerate the movement of said movable contact into engagement with said fixed contact.

References Cited in the tile of this patent UNITED STATES PATENTS 2,570,998 Wolif a Oct. 9, 1951 2,795,678 Mertler June 1l, 1957 2,833,893 Weber May 6, 1958 l Y FOREIGN PATENTS 481,641 Germany .Y Aug. 24, 1929 771,466 France July 23, 1934 b 540,529 Y 1941 o Great Britain Oct. 21, 

1. A SWITCH MECHANISM COMPRISING: (A) SUPPORT MEANS, (B) A FIXED CONTACT MOUNTED ON SAID SUPPORT MEANS, (C) A FLEXIBLE SPRING ARM HAVING ONE END SECURED TO SAID SUPPORT MEANS, (D) A MOVABLE CONTACT CARRIED ON THE OTHER END OF SAID SPRING ARM AND NORMALLY URGED BY SAID SPRING ARM IN A FIRST DIRECTION TOWARD SAID FIXED CONTACT, (E) AN ELONGATED ACTUATOR MEMBER FORMED OF A RELATIVELY RIGID MATERIAL WITH RESPECT TO SAID SPRING ARM AND HAVING ONE END FIXED TO THE END OF SAID SPRING ARM ON WHICH SAID MOVABLE CONTACT IS CARRIED, AND EXTENDING ALONG ONE SIDE OF SAID SPRING ARM REMOTE FROM SAID FIXED CONTACT AND HAVING THE OTHER END TERMINATING ADJACENT SAID ONE END OF SAID SPRING ARM AND BEING MOVABLE LATERALLY THEREFROM, (F) SAID SPRING ARM NORMALLY BIASING SAID ACTUATOR MEMBER TOWARD SAID SPRING ARM, AND (G) MEANS FOR APPLYING A MOVING FORCE TO SAID ACTUATOR MEMBER BETWEEN THE ENDS THEREOF IN A DIRECTION OPPOSITE TO SAID ONE DIRECTION SO AS TO TEND TO SEPARATE SAID OTHER END OF SAID ACTUATOR MEMBER FROM SAID SPRING ARM AND FLEX SAID CONTACT CARRYING END OF SAID SPRING ARM TO IMPART A ROLLING ACTION OF SAID MOVABLE CONTACT ON SAID FIXED CONTACT BEFORE SAID MOVBLE CONTACT IS MOVED AWAY FROM SAID FIXED CONTACT. 